Transport pipes (especially liquid transport pipes) are known to become infested with many forms of build up, including tubercles in a case of municipal water pipes. The pipes become sclerotic and continually narrow as tubercles build up. Regardless of pipe type (gas/liquid/solid transport), flow eventually occludes with tubercle residue and other build up. Few viable industrial and commercial solutions are available to deal with sclerotic pipes quickly and effectively.
One option is to replace infected pipes, but this is frequently unnecessary, time consuming, impractical in urban areas and established neighbourhoods, expensive, and results in an additional problem of waste pipe disposal.
Another option is to accelerate abrasive projectiles (like rocks of progressive calibre) through infected pipes. A pipe is pressurized with a gas stream, and abrasive projectiles are fed into the stream. The streaming projectiles strike and break away protruding tubercle portions, and discharge out of the pipe along with broken tubercles. The streaming projectiles can also be used to clean away old linings, film, and tar residue. In this option, feeding projectiles from a hopper to a pressurized pipe is particularly difficult. Apart from pressure differential concerns (that can present a safety hazard), the projectiles must be metered in a manner that prevent clogging of the system, and also in a manner that minimizes or altogether eliminates dust emission (from projectile handling and metering). Dust emissions reduce the dispensing system's lifespan.
In an example, one system, disclosed in PCT/GB2007/003369 (published as WO/2008/029149), uses an auger to metre projectiles from a hopper into a pipe. One major difficulty with this system is that it requires all of the hopper, conveyor (in this instance an auger), and outlet pipe to be pressurized (so projectiles cannot be fed into the outlet pipe while, for example, the hopper is at a pressure (like atmospheric pressure) lower than that of the pipe). Another significant difficulty is that, in practise, the projectiles tend to clog the auger relatively easily (because of the auger's axle and the blade configuration projecting therefrom—ie a pocket or confined area is formed where projectiles can gather and clog). The auger also tends to (in the case where the projectiles are stones) confine, compress and crush stones, resulting in dust emission (altogether generally referred to as confined projectile handling). Compression and crushing also interfere with the pipe's ultimate cleaning, to say nothing of damaging the auger itself (wear and tear).